A control system automatically operates a subsea well control device on detecting that a load in an Intervention Riser System (IRS) coupled to the subsea well control device has reached a threshold. The control system has a first control unit to detect that the load in the IRS has reached the threshold and a second control unit triggering actuation of the subsea well control device. The first control unit is in communication with the second control unit and issues an activation command to the second control unit to cause it to trigger actuation of the subsea well control device. The first control unit automatically issues the activation command to the second control unit upon detecting that the load in the IRS has reached the threshold, to trigger actuation of the subsea well control device prior to structural failure of an IRS.